Fatigue-free bipolar loop treatment to reduce imprint effect in piezoelectric device

ABSTRACT

In some embodiments, the present disclosure relates to a method in which a first set of one or more voltage pulses is applied to a piezoelectric device over a first time period. During the first time period, the method determines whether a performance parameter of the piezoelectric device has a first value that deviates from a reference value by more than a predetermined value. Based on whether the first value deviates from the reference value by more than the predetermined value, the method selectively applies a second set of one or more voltage pulses to the piezoelectric device over a second time period. The second time period is after the first time period and the second set of one or more voltage pulses differs in magnitude and/or polarity from the first set of one or more voltage pulses.

REFERENCE TO RELATED APPLICATION

This Application is a Continuation of U.S. application Ser. No.16/534,330, filed on Aug. 7, 2019, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

Piezoelectric devices (e.g., piezoelectric actuators, piezoelectricsensors, etc.) are used in many modern day electronic devices (e.g.,automotive sensors/actuators, aerospace sensors/actuators, etc.). Oneexample of a piezoelectric device is a piezoelectric actuator. Apiezoelectric actuator can be utilized to create a physical movementthat exerts a force on a physical part in a system under the control ofan electrical signal. The physical movement generated by thepiezoelectric actuator can be utilized to control various kinds ofsystems (e.g., mechanical systems, optical systems, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of apiezoelectric device coupled to control circuitry.

FIG. 2 illustrates a cross-sectional view of some embodiments of apiezoelectric device coupled to bias circuitry and measurementcircuitry.

FIG. 3 illustrates a plot of some embodiments of a polarization curveand a bipolar loop within the polarization curve to recover a degradedpiezoelectric device.

FIGS. 4, 5 and 6 illustrate timing diagrams of some embodiments ofvoltage versus time for a bipolar loop recovery operation after one ormore pulses in a performance operation.

FIG. 7A illustrates of a plot of some embodiments of recovery ofpermittivity of a piezoelectric structure after an imprint effect due tomultiple performance operation cycles.

FIGS. 7B and 7C illustrate timing diagrams of some embodiments ofperformance operations and bipolar loops that may correspond to the plotof FIG. 7A.

FIG. 8A illustrates a plot of some embodiments of recovery ofpermittivity of a piezoelectric structure to prevent an imprint effect.

FIGS. 8B and 8C illustrate timing diagrams of some embodiments ofperformance operations and bipolar loops that may correspond to the plotof FIG. 8A.

FIG. 9 illustrates a flow diagram of some embodiments of a method ofperforming a bipolar loop after a performance parameter of apiezoelectric device has degraded.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

A piezoelectric metal-insulator-metal (MIM) device includes apiezoelectric layer arranged between top and bottom electrodes. When asufficient voltage bias is applied across the top and bottom electrodes,a mechanical strain may be induced in the piezoelectric layer. Themechanical strain may, for example, be used in acoustical, mechanical,and/or optical applications. The change in the structure of thepiezoelectric layer may affect other electronic properties in thepiezoelectric layer such as permittivity, capacitance, polarization,etc.

Over time, as voltage pulses are applied across the piezoelectric layerduring a performance mode of the device, electrical charges mayaccumulate at an interface between the piezoelectric layer and the topor bottom electrode. The electrical charge accumulation, also known asan imprint effect (e.g., static imprint or dynamic imprint), may degradedevice performance of the piezoelectric MIM device. Static imprint mayoccur after a voltage bias pulse is applied to the piezoelectric MIMdevice, and then the piezoelectric MIM device is stored for a longperiod of time. Dynamic imprint may occur after consecutive unipolarbias pulses are applied to the piezoelectric MIM device. For example, ifthe imprint effect (e.g., static imprint or dynamic imprint) occurs in apiezoelectric MIM device, properties such as the permittivity,capacitance, polarization and/or piezoelectric coefficient, for example,of the piezoelectric layer may significantly change when no voltage biasis applied to the piezoelectric MIM device, thereby degrading thepiezoelectric MIM device performance. Thus, degradation of electrical ormechanical properties such as permittivity, capacitance, polarization,piezoelectric coefficient, or the like may be used to quantify a degreeof imprint of a piezoelectric MIM device.

Various embodiments of the present disclosure provide a method forrecovering or preventing a degraded piezoelectric MIM device. In someembodiments, over a first time period, a piezoelectric device may beoperated in a performance mode, which may comprise the application ofone or more voltage biases and/storage of the piezoelectric device. Arecovery operation comprising a bipolar loop, may be performed after aperformance parameter of the piezoelectric device has reached apredetermined threshold value. The predetermined threshold value mayindicate that the imprint effect has occurred in the piezoelectricdevice, or that the imprint effect is about to occur in thepiezoelectric device.

Upon detection of the predetermined threshold value, one or more cyclesof the bipolar loop may be conducted to recover the degradedpiezoelectric device. The bipolar loop may comprise the application of avoltage bias at a first amplitude having a first polarity. The voltagebias is then adjusted to a second amplitude having a second polarityopposite to the first polarity, wherein a magnitude of the firstamplitude is equal to a magnitude of the second amplitude. The voltagebias may then be adjusted to a third amplitude equal to zero. Themagnitude of the first amplitude, in some embodiments, is less than orequal to an electric coercive field voltage of the piezoelectric deviceprior to degradation. By applying the bipolar loop to the piezoelectricdevice, charge accumulation at an interface between the piezoelectriclayer and the top or bottom electrode may be reduced, and degradedproperties of the piezoelectric device caused by an imprint effect(e.g., static imprint or dynamic imprint) may be recovered. Because thevoltage biases of the bipolar loop have amplitudes less than or equal tothe electric coercive field voltage of the piezoelectric device, thestructure of the piezoelectric device does not experience fatigue. Thus,the bipolar loop may restore or improve reliability of the piezoelectricdevice performance without degrading the mechanical structure of thepiezoelectric device through fatigue.

FIG. 1 illustrates a cross-sectional view 100 of some embodiments of apiezoelectric device coupled to control circuitry.

The piezoelectric device in cross-sectional view 100 may comprise, insome embodiments, a bottom electrode 104 over a substrate 102. Apiezoelectric layer 106 may be arranged over the bottom electrode 104and beneath a top electrode 108. In some embodiments, a passivationlayer 110 may be arranged over a top surface of the top electrode 108and cover outer sidewalls of the top electrode 108, the piezoelectriclayer 106, and the bottom electrode 104. In some embodiments, the bottomelectrode 104 may be wider than the piezoelectric layer 106 and the topelectrode 108, and the piezoelectric layer 106 and the top electrode 108may have outermost sidewalls that are substantially aligned with oneanother. A first metal pad 112 a may be arranged over the top electrode108 and extend through the passivation layer 110 to directly contact thetop electrode 108. The first metal pad 112 a is spaced apart from thepiezoelectric layer 106 and the bottom electrode 104 by the passivationlayer 110. In some embodiments, the first metal pad 112 a is also overthe substrate 102. A second metal pad 112 b may be arranged over thebottom electrode 104 and extend through the passivation layer 110 todirectly contact the bottom electrode 104. In some embodiments, thesecond metal pad 112 b is spaced apart from the piezoelectric layer 106and/or the top electrode 108 by the passivation layer 110. In someembodiments, the second metal pad 112 b is also over the substrate 102.The second metal pad 112 b is separated from the first metal pad 112 a.In some embodiments, electrical contacts 114 are coupled to each of thefirst metal pad 112 a and the second metal pad 112 b. In someembodiments, the electrical contacts 114 are solder bumps.

In some embodiments, the first metal pad 112 a and the second metal pad112 b each extend through openings in the passivation layer 110. In someembodiments, a width of the openings in the passivation layer 110 mayeach be in a range of between about 10 micrometers and about 50micrometers, about 50 micrometers and about 100 micrometers, about 100micrometers and about 500 micrometers, about 500 micrometers and about10 millimeters, and about 10 millimeters and about 100 millimeters.Further, in some embodiments, the passivation layer 110, the topelectrode 108, the piezoelectric layer 106, the bottom electrode 104,and the first and second metal pads 112 a, 112 b may each have athickness in a range of between about 10 angstroms and about 100angstroms, about 100 angstroms and about 100 nanometers, about 100nanometers and about 1 micrometer, about 1 micrometer and about 100micrometers, and about 100 micrometers and about 1 millimeter.

In some embodiments the bottom electrode 104 and the top electrode 108may each comprise, for example, stainless steel, brass, copper,galvanized iron, mild steel, lead, monel, nickel, nickel-chromium, zinc,phosphor bronze, aluminum, platinum, gold, ruthenium, copper alloy,graphite, calcium, cesium carbonate, lithium fluoride, molybdenum (IV)oxide, silver, carbon, palladium, tin, steel, scandium, titanium,vanadium, chromium, manganese, cobalt, zinc, gallium, indium, thallium,doped silicon, polysilicon, germanium, antimony, tungsten, hafnium,iridium, mixed metal oxide, titanium nitride, tantalum nitride, or thelike. In some embodiments, the bottom electrode 104 comprises the samematerials as the top electrode 108, whereas in other embodiments, thebottom electrode 104 may comprise a different material than the topelectrode 108. In some embodiments, the piezoelectric layer 106 maycomprise, for example, lead zirconate titanate, aluminum nitride,lithium niobate, gallium arsenide, zinc oxide, quartz single crystals,polymer-film piezoelectrics (e.g., PVDF), some other piezoelectricmaterial, or a combination of the foregoing.

Further, in other embodiments of a piezoelectric device, thepiezoelectric layer 106 may be disposed between the top and bottomelectrodes 108, 104. The piezoelectric layer 160, the bottom electrode104, and the top electrode 108 may be surrounded by an inter-layerdielectric layer. Further, in such other embodiments, vias may becoupled to the top and bottom electrodes 108, 104 instead of the firstand second metal pads 112 a, 112 b.

In some embodiments, control circuitry 120 may be coupled to theelectrical contacts 114 via wires 116. Thus, the control circuitry 120may be coupled to the bottom electrode 104 and the top electrode 108.The control circuitry 120 is configured to apply voltage biases acrossthe piezoelectric layer 106 via the bottom electrode 104 and the topelectrode 108. For example, in some embodiments, the bottom electrode104 is grounded, and the control circuitry 120 is configured to applyvoltages to the top electrode 108.

In some embodiments, the control circuitry 120 is configured to operatethe piezoelectric device in a performance mode and a recovery mode. Theperformance mode involves the control circuitry 120 applying voltagebias pulses across the piezoelectric layer 106 to induce a mechanicalstrain in the piezoelectric layer 106. During the performance mode,charge carriers may accumulate at a first interface 124 which is betweenthe piezoelectric layer 106 and the bottom electrode 104, or chargecarriers may accumulate at a second interface 128 which is between thepiezoelectric layer 106 and the top electrode 108. For example, in someembodiments, multiple voltage biases having a same polarity may beapplied across the piezoelectric layer 106 by the control circuitry 120.Thus, charge carriers may be continuously biased in a certain direction(e.g., from the bottom electrode 104 to the top electrode 108 or fromthe top electrode 108 to the bottom electrode 104) depending on thepolarity, and charge carriers may accumulate at the first or secondinterface 124, 128, thereby degrading the piezoelectric deviceperformance. In other embodiments, the piezoelectric device may bestored for a long period of time, and charge carriers may accumulate atone of the first or second interfaces 124, 128, and degrade thepiezoelectric device performance.

To improve the piezoelectric device performance, the control circuitry120 may be configured to operate in a recovery mode by applying abipolar loop using bipolar voltage biases that are less than or equal toan electric coercive field voltage of the piezoelectric layer 106. Insome embodiments, the control circuitry 120 is configured to apply thebipolar loop multiple times to improve the piezoelectric deviceperformance by decreasing charge carrier accumulation at the first orsecond interface 124, 128.

FIG. 2 illustrates a cross-sectional view 200 of some embodiments of apiezoelectric device coupled to measurement circuitry and biascircuitry.

In some embodiments, the control circuitry 120 of FIG. 1 may comprisebias circuitry 210 and measurement circuitry 220. Thus, in someembodiments, measurement circuitry 220 and bias circuitry 210 may becoupled to the top electrode 108 and the bottom electrode 104. Further,in some embodiments, the measurement circuitry 220 may be coupled to thebias circuitry 210. In other embodiments, the measurement circuitry 220may be directly coupled to the bias circuitry 210, but not directlycoupled to the bottom and top electrodes 104, 108 of the piezoelectricdevice.

In some embodiments, the bias circuitry 210 may be configured to applyvoltage biases of varying magnitudes, polarities, and/or time periodsacross the piezoelectric layer 106 to operate in the performance and therecovery modes. The measurement circuitry 220 may be configured todetermine when the bias circuitry 210 is to operate in the recoverymode. In some embodiments, the measurement circuitry 220 is configuredto detect that a performance parameter of the piezoelectric device hasreached or deviated from a predetermined threshold value. For example,in some embodiments, the performance parameter may be an electricalproperty of the piezoelectric layer 106, such as, for example,permittivity, capacitance, polarization, or piezoelectric coefficient.In some embodiments, the predetermined threshold value is before imprinthas occurred, whereas in other embodiments, the predetermined thresholdvalue is after imprint has occurred. For example, in some embodiments,the predetermined threshold value may define degradation of capacitance.In such embodiments, the capacitance may be considered degraded when thecapacitance of the piezoelectric device has deviated from a referencevalue by more than the predetermined threshold value, such as, forexample, 4 percent. In some embodiments, the reference value may be aninitial value of the performance parameter of the piezoelectric device.Nevertheless, once the measurement circuitry 220 detects degradation,the measurement circuitry 220 may signal to the bias circuitry 210 toapply the bipolar loop to recover the piezoelectric device.

In other embodiments, the performance parameter of the piezoelectricdevice may be a predetermined performance time or a predetermined numberof performance pulses. For example, in some embodiments, the measurementcircuitry 220 may count the time that the bias circuitry 210 has beenoperating in performance mode. Upon the detection by the measurementcircuitry 220 that the time has reached the predetermined performancetime, the measurement circuitry 220 may signal to the bias circuitry 210to apply the bipolar loop to recover the piezoelectric device. Forexample, in some embodiments, the predetermined performance time may beminutes, hours, days, weeks, etc. Further, in some embodiments, thepredetermined number of performance pulses may range from one tothousands of pulses.

In some embodiments, the bias circuitry 210 is configured to apply thebipolar loop multiple times to increase the recovery of thepiezoelectric device. In some embodiments, the number of bipolar loopsconducted in a recovery operation by the bias circuitry 210 ispredetermined. In other embodiments, the measurement circuitry 220 maymeasure the performance parameter of the piezoelectric device, anddetect when the performance parameter has recovered. In someembodiments, recovery of the performance parameter may be based on, forexample, a predetermined recovered performance value or a percentimprovement between the predetermined threshold value and theperformance parameter. In other embodiments, the number of bipolar loopsconducted may be based on a predetermined number of loops or apredetermined time period.

FIG. 3 illustrates a plot 300 of some embodiments of a bipolar loop inrelation to a hysteresis loop of a piezoelectric device.

Plot 300 illustrates polarization versus voltage of a piezoelectricdevice, such as the piezoelectric device illustrated in FIGS. 1 and 2 ,for example. An electrical coercive field of a piezoelectric material isthe maximum electric field that the piezoelectric material can toleratebefore becoming depolarized. The plot 300 in FIG. 3 utilizes a thicknessof the piezoelectric layer such that the electrical coercive field maybe quantified as an electrical coercive field voltage in a hysteresisloop 302. The hysteresis loop 302 represents the change in polarizationof a piezoelectric device as the voltage bias applied to thepiezoelectric device is increased from zero volts to a first positivevoltage 316, decreased to a first negative voltage 306, and increasedback to zero volts, for example. The electrical coercive field voltageof the piezoelectric device is the voltage at which the polarization isequal to zero. In many embodiments, as illustrated in FIG. 3 , apiezoelectric device has a positive electric coercive field voltage 314and a negative electric coercive field voltage 308 determined by thehysteresis loop 302 prior to any imprint effects (e.g., static imprintor dynamic imprint). In some embodiments, the positive electric coercivefield voltage 314 and the negative electric coercive field voltage 308are equal in magnitude. For example, in some embodiments, the positiveelectric coercive field voltage 314 may be approximately 3 volts, andthe negative electric coercive field voltage 308 may be approximately −3volts.

In some embodiments, a bipolar loop 304 is applied to the piezoelectricdevice in a recovery operation. The maximum voltage bias and minimumvoltage bias of the bipolar loop 304 are determined by the positiveelectric coercive field voltage 314 and the negative electric coercivefield voltage 308, respectively. Thus, in some embodiments, to apply thebipolar loop 304 to a degraded piezoelectric device, the voltage biasapplied to the piezoelectric device by the control circuitry (120 ofFIG. 1 ) may, for example, be increased from a start voltage (e.g., zerovolts) to the positive electric coercive field voltage 314, decreased tothe negative electric coercive field voltage 308, and increased to anend voltage (e.g., zero volts) equal to the start voltage. In otherembodiments, the bipolar loop 304 has a maximum voltage that is lessthan the positive electric coercive field voltage 314 and a minimumvoltage that is greater than the negative electric coercive fieldvoltage 308. Thus, the maximum and minimum voltages of the bipolar loop304 equal to or between the positive electric coercive field voltage 314and the negative electric coercive field voltage 308 to recover thedegraded piezoelectric device while preventing fatigue in thepiezoelectric layer 106.

FIG. 4 illustrates a timing diagram 400 of some embodiments where abipolar loop is applied after consecutive unipolar pulses applied to apiezoelectric device.

In some embodiments, during a performance mode, control circuitry (120of FIG. 1 ) may apply multiple unipolar pulses 402. Each pulse 404 ofthe multiple unipolar pulses 402 may have a first amplitude that issustained over a first time period t₁. In some embodiments, asillustrated in FIG. 4 , the first amplitude may be equal to the firstpositive voltage 316, for example, or in some embodiments, equal to thefirst negative voltage 306. In other embodiments, the first amplitudemay be greater than or less than the first positive voltage 316. In someembodiments, the first positive voltage 316 may be greater than thepositive electric coercive field voltage 314, and the first negativefield voltage 306 may be less than the negative electric coercive fieldvoltage 308. However, increasing the first amplitude may increase therate of degradation of performance parameters of the piezoelectricdevice. Further in some embodiments, each pulse 404 may have the samefirst amplitudes and/or first time periods t₁, whereas in otherembodiments, the first amplitude and/or the first time period t₁ of eachpulse 404 may be different. However, each pulse 404 has a same polarity,which may cause dynamic imprint in a piezoelectric device.

Thus, in some embodiments, after multiple unipolar pulses 402 have beenapplied to a piezoelectric device over a second time period t₂, arecovery operation comprising the bipolar loop 304 may be applied to thepiezoelectric device such to recover or prevent the piezoelectric devicefrom the dynamic imprint effect. To conduct the bipolar loop 304,control circuitry (120 of FIG. 1 ) may increase a voltage bias appliedto the piezoelectric device to a second amplitude having a firstpolarity that is sustained for a fourth time period t₄, decrease thevoltage bias to a third amplitude having a second polarity that issustained for the fourth time period t₄, and increase the voltage biasfrom the third amplitude to zero. In some embodiments, the secondamplitude equals the third amplitude, and the first polarity is oppositeto the second polarity. The first and second amplitudes have magnitudesthat are less than or equal to magnitudes of the positive and negativeelectric coercive field voltages 308, 314 of the piezoelectric device.In FIG. 4 , the positive electric coercive field voltage 314 is appliedfirst, and then the negative electric coercive field voltage 308 may beapplied. In other embodiments, the negative electric coercive fieldvoltage 308 may be applied first, and then the positive electriccoercive field voltage 314 may be applied. Nevertheless, the bipolarloop 304 over a third time period t₃ may be applied after multipleunipolar pulses 402 have been applied to a piezoelectric device torecover a piezoelectric device from dynamic imprint effects.

FIG. 5 illustrates a timing diagram 500 of some embodiments where abipolar loop is applied after a piezoelectric device undergoes a longstorage time to recover the piezoelectric device.

In some embodiments, during a performance mode, control circuitry (120of FIG. 1 ) may apply a static sequence 502 comprising a pulse 504followed by a long storage time step 506 to a piezoelectric device. Likeeach pulse 404 in FIG. 4 , in some embodiments, the pulse 504 in FIG. 5may have a first amplitude that is sustained over the first time periodt₁. In some embodiments, the first amplitude is equal to the firstpositive voltage 316, for example, or the first negative voltage 306. Inother embodiments, the first amplitude may be greater than or less thanthe first positive voltage 316, or greater than or less than the firstnegative voltage 306. After the first time period t₁, the controlcircuitry (120 of FIG. 1 ) may not apply a voltage bias to thepiezoelectric device for a fifth time period t₅ during a long storagetime step 506. In some embodiments, the fifth time period t₅ may begreater than the first time period t₁. Nevertheless, in some embodimentsthe long storage time step 506 (e.g., Q-time) may cause static imprintin a piezoelectric device, thereby degrading properties of thepiezoelectric device. In some embodiments, to restore the degradedproperties of the piezoelectric device from the static imprint effect,the bipolar loop may be performed over the third time period t₃ afterthe long storage time step 506.

FIG. 6 illustrates a timing diagram 600 of some embodiments where abipolar loop is applied before a piezoelectric device undergoes a longstorage time to prevent degradation in a piezoelectric device.

The timing diagram 600 of FIG. 6 comprises the same pulse 504, bipolarloop 304, and long storage time step 506 as in the timing diagram 500 ofFIG. 5 , except that in FIG. 6 , the bipolar loop 304 is conductedbefore the long storage time step 506. In some embodiments, the bipolarloop 304 is conducted before the long storage time step 506 to preventthe static imprint effect from occurring in a piezoelectric device byreducing the polarization and therefore charge accumulation at a firstor second interface (e.g., 124, 128) of the piezoelectric device duringthe long storage time step 506.

FIG. 7A illustrates a plot 700A of some embodiments of degradation,imprint, and recovery of permittivity of a piezoelectric device.

The plot 700A in FIG. 7A comprises multiple permittivity data points 606for each “test number.” In some embodiments, a test may comprisemultiple unipolar pulses (402 of FIG. 4 ), a static sequence (502 ofFIG. 5 ), or a combination thereof. For example, in some embodiments, atest may comprise multiple unipolar pulses (402 of FIG. 4 ) followed bya long storage time step 506. After each test, the permittivity or someother performance parameter of a piezoelectric device may be measured atzero volts and recorded on the plot 700A as a permittivity data point606. A first group 702 of the permittivity data points 606 illustrateshow over time, the permittivity of a piezoelectric device decreases.However, between the first group 702 and a second group 602, thepermittivity of a piezoelectric device significantly decreases to animprinted permittivity 706, and remains constant throughout thepermittivity data points 606 of the second group 602. Thus, an imprinteffect (e.g., static imprint or dynamic imprint) may have occurredbetween the last test of the first group 702 and a first test of thesecond group 602.

In some embodiments, at the end of the second group 602, a recoveryoperation 604 comprising bipolar loops (e.g., 304 of FIG. 4 ) mayincrease the permittivity of the piezoelectric device. Although therecovery operation 604 may not fully recover the permittivity of thepiezoelectric device to an initial permittivity 708, the recoveryoperation 604 may increase the permittivity of the piezoelectric devicefrom the imprinted permittivity 706 to a recovered permittivity 707. Insome embodiments, the imprinted permittivity 706 is ten percent lowerthan the initial permittivity 708. Thus, although the permittivity datapoints 606 may not be as high in a third group after the recoveryoperation 604 than the permittivity data points 606 in the first group702, the recovery operation 604 still improves performance parameters ofthe piezoelectric device after imprint effects.

FIG. 7B illustrates a timing diagram 700B of some embodiments ofperforming a bipolar loop to recover a piezoelectric device after staticimprint.

The timing diagram 700B of FIG. 7B may correspond to the plot 700A ofFIG. 7A. For example, in some embodiments, each permittivity data point606 of FIG. 7A may represent the measured permittivity of apiezoelectric device after each static sequence 502. Thus, in the firstgroup 702 of FIG. 7A, there are nine permittivity data points 606, andin the first group 702 of FIG. 7B, there are nine static sequences 502.In some embodiments, the first group 702 of static sequences 502 mayoccur over a sixth time period t₆, and the second group 602 of staticsequences 502 may occur over a seventh time period t₇. Between the firstand second groups 702, 602, a static imprint effect may occur. Torecover the piezoelectric device from the static imprint effect, therecovery operation 604 may comprise more than one bipolar loop 304. Forexample, as illustrated in FIG. 7B, ten bipolar loops 304 are conductedover an eighth time period t₈ in the recovery operation 604. In otherembodiments, a total number of bipolar loops 304 in a recovery operation604 may be in a range of between approximately one bipolar loop 304 andapproximately 100 bipolar loops 304.

In some embodiments, a total number of bipolar loops 304 conducted in arecovery operation 604 is dependent how much time can be spared, howmuch recovery is desired, and/or the amount of power available, forexample. In some embodiments, each bipolar loop 304 occurs over thethird time period t₃ that is equal to approximately 40 milliseconds, forexample. In some embodiments, the bipolar loops 304 continue untilmeasurement circuitry (220 of FIG. 2 ) determines that a predeterminedrecovered performance value has been reached, or a percent improvementbetween the predetermined threshold value and the performance parameterhas been reached. The predetermined recovered performance value may bebased on a measurement of a performance parameter of the piezoelectricdevice, the eighth time period t₈, or a number of bipolar loops, forexample. Thus, by using one or more bipolar loops 304 in a recoveryoperation 604, properties of a degraded piezoelectric device due to animprint effect may be improved.

FIG. 7C illustrates a timing diagram 700C of some embodiments ofperforming a bipolar loop to recover a piezoelectric device afterdynamic imprint.

The timing diagram 700C of FIG. 7C may correspond to the plot 700A ofFIG. 7A. For example, in some embodiments, each permittivity data point606 of FIG. 7A may represent the measured permittivity of apiezoelectric device after each set of multiple unipolar pulses 402. Insome embodiments, each set of multiple unipolar pulses 402 may comprisethree pulses (404 of FIG. 4 ), whereas in other embodiments, each set ofmultiple unipolar pulses 402 may comprise more than or less than threepulses (404 of FIG. 4 ). In the first group 702 of FIG. 7A, there arenine permittivity data points 606, and in the first group 702 of FIG.7C, there are nine sets of multiple unipolar pulses 402. Between thefirst and second groups 702, 602, a dynamic imprint effect may occur. Torecover the piezoelectric device from the dynamic imprint effect, therecovery operation 604 may comprise more than one bipolar loop 304.

FIG. 8A illustrates a plot 800A of some embodiments of recovery ofpermittivity of a piezoelectric device prior to imprint effects.

The plot 800A of FIG. 8A illustrates how the recovery operation 604 maybe applied after the first group 702 but before the second group (602 ofFIG. 7A) such that the piezoelectric device may recover before animprint effect (e.g., static imprint or dynamic imprint) occurs.Although the imprint effect has not fully occurred, as shown in thesecond group (602 of FIG. 7A), the permittivity of the piezoelectricdevice may still degrade. In some embodiments, by preventing the imprinteffect, the recovery operation 604 may be more effective in improvingdegraded device performance of a piezoelectric device.

In some embodiments, the recovery operation 604 may be applied to apiezoelectric device because the intermediate permittivity 710 or someother performance parameter of the piezoelectric device has reached aperformance parameter predetermined threshold value. In otherembodiments, the recovery operation 604 may be applied to thepiezoelectric device because the intermediate permittivity 710 of thepiezoelectric device has deviated from the initial permittivity 708(e.g., reference value) by more than a performance parameterpredetermined threshold value. In some embodiments, the measurement anddetermination of device degradation may be performed by measurementcircuitry (220 of FIG. 2 ). In yet other embodiments, when a totalnumber of pulses or a time period has reached a predetermined thresholdvalue while the piezoelectric device is in performance mode during thefirst group 702, the recovery operation 604 may be conducted to preventthe imprint effect (e.g., static imprint or dynamic imprint).

FIG. 8B illustrates a timing diagram 800B of some embodiments ofperforming a bipolar loop prior to degradation of a piezoelectric devicevia static imprint.

The timing diagram 800B of FIG. 8B may correspond to the plot 800A ofFIG. 8A. For example, in some embodiments, each permittivity data point606 of FIG. 8A may represent the measured permittivity of apiezoelectric device after each static sequence 502. Thus, in the firstgroup 702 of FIG. 8A, there are nine permittivity data points 606, andin the first group 702 of FIG. 8B, there are nine static sequences 502.However, a last one 802 of the static sequences 502 may not comprise thelong storage time step 506.

In some embodiments, because the recovery operation 604 is conductedbefore the static imprint effect, less bipolar loops 304 may be used inthe recovery operation 604 than if the recovery operation 604 wasperformed after the static imprint effect (e.g., FIG. 7B). Inembodiments, to better improve the piezoelectric device, a same or ahigher number of bipolar loops 304 may be used in the recovery operation604 when conducted before the static imprint effect than the number ofbipolar loops 304 conducted after a static imprint effect.

FIG. 8C illustrates a timing diagram 700B of some embodiments ofperforming a bipolar prior to degradation of a piezoelectric device viadynamic imprint.

The timing diagram 800C of FIG. 8C may correspond to the plot 800A ofFIG. 8A. For example, in some embodiments, each permittivity data point606 of FIG. 8A may represent the measured permittivity of apiezoelectric device after each set of multiple unipolar pulses 402.Thus, in the first group 702 of FIG. 8A, there are nine permittivitydata points 606, and in the first group 702 of FIG. 8B, there are ninesets of multiple unipolar pulses 402. In some embodiments, to preventdynamic imprint from occurring and to improve any performance parametersof the degraded piezoelectric device, the recovery operation 604 may beconducted after the first group 702.

FIG. 9 illustrates a flow diagram of some embodiments of a method 900 ofperforming a bipolar loop to a piezoelectric device upon detection of aperformance parameter reaching a predetermined threshold value.

While method 900 is illustrated and described below as a series of actsor events, it will be appreciated that the illustrated ordering of suchacts or events are not to be interpreted in a limiting sense. Forexample, some acts may occur in different orders and/or concurrentlywith other acts or events apart from those illustrated and/or describedherein. In addition, not all illustrated acts may be required toimplement one or more aspects or embodiments of the description herein.Further, one or more of the acts depicted herein may be carried out inone or more separate acts and/or phases.

At act 902, a piezoelectric device is operated in performance mode byapplying one or more voltage pulses at a first amplitude to thepiezoelectric device. FIG. 4 illustrates a timing diagram 400 of someembodiments corresponding to act 902.

At act 904, a determination that a performance parameter of thepiezoelectric device has reached a predetermined threshold value isperformed.

At act 906, a bipolar loop is applied to the piezoelectric device byperforming acts 906 a, 906 b, and 906 c.

At act 906 a, a first voltage bias is applied to the piezoelectricdevice, wherein the first voltage bias has a first polarity and a secondamplitude.

At act 906 b, the first voltage bias is adjusted to a second voltagebias, wherein the second voltage bias has the second amplitude and asecond polarity opposite to the first polarity.

At act 906 c, the second voltage bias is adjusted to a third voltagebias equal to zero. FIGS. 8A, 8B, and 8C illustrate a plot 800A, atiming diagram 800B, and a timing diagram 800C, respectively, of someembodiments corresponding to acts 904, 906, 906 a, 906 b, and 906 c.

Therefore, the present disclosure relates to a method of performing abipolar loop to a piezoelectric device to prevent an imprint effect orrecover after an imprint effect to reduce degradation and increasereliability of a piezoelectric device.

Accordingly, in some embodiments, the present disclosure relates to amethod for recovering degraded device performance of a piezoelectricdevice, the method comprising: operating the piezoelectric device in aperformance mode over a first time period by applying one or morevoltage pulses greater than or equal to a first amplitude to thepiezoelectric device; determining during the first time period that aperformance parameter of the piezoelectric device has a first value thathas deviated from a reference value by more than a predeterminedthreshold value; applying a bipolar loop to the piezoelectric deviceover a second time period comprising positive and negative voltagebiases, the second time period being after the first time period; andoperating the piezoelectric device in the performance mode over a thirdtime period after the second time period, wherein the performanceparameter of the piezoelectric device has a second value during thethird time period, and wherein an absolute difference between the secondvalue and the reference value is less than an absolute differencebetween the first value and the reference value.

In other embodiments, the present disclosure relates to a method forpreventing degraded device performance of a piezoelectric device, themethod comprising: operating the piezoelectric device in a performancemode over a first time period by applying one or more voltage pulsesgreater than or equal to a first amplitude to the piezoelectric device,wherein the first amplitude is greater than an electric coercive fieldvoltage of the piezoelectric device; determining that a predeterminedthreshold value of the performance mode has been reached; and performinga bipolar loop to the piezoelectric device over a second time period by:applying a voltage bias signal across the piezoelectric device at asecond amplitude at a first polarity; adjusting the voltage bias signalacross the piezoelectric device from the second amplitude to a thirdamplitude at a second polarity opposite to the first polarity, whereinthe second amplitude is equal to the third amplitude, and wherein thesecond amplitude is less than or equal to the electric coercive fieldvoltage of the piezoelectric device; and adjusting the voltage biassignal across the piezoelectric device from the third amplitude to afourth amplitude that is between the second amplitude and the thirdamplitude.

In yet other embodiments, the present disclosure relates to a system,the system comprising: a piezoelectric device disposed on asemiconductor substrate, the piezoelectric device comprising apiezoelectric structure disposed between a first electrode and a secondelectrode; bias circuitry electrically coupled to the first electrodeand the second electrode, wherein the bias circuitry configured tooperate in a performance mode by applying a voltage bias across thepiezoelectric structure; measurement circuitry electrically coupled tothe bias circuitry, wherein the measurement circuitry is configured todetect that a predetermined threshold value has been reached during theperformance mode; and wherein the bias circuitry is configured toperform a recovery operation upon detection of the predeterminedthreshold value by: increasing the voltage bias from a start value to afirst magnitude at a first polarity, decreasing the voltage bias fromthe first magnitude at the first polarity to the first magnitude at asecond polarity opposite to the first polarity, and increasing thevoltage bias from the first magnitude at the second polarity to an endvalue equal to the start value.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method, comprising: applying a first set of oneor more voltage pulses to a piezoelectric device over a first timeperiod; during the first time period, determining whether a performanceparameter of the piezoelectric device has a first value that deviatesfrom a reference value by more than a predetermined value; and based onwhether the first value deviates from the reference value by more thanthe predetermined value, selectively applying a second set of one ormore voltage pulses to the piezoelectric device over a second timeperiod, the second time period being after the first time period andsecond set of one or more voltage pulses differing in magnitude and/orpolarity from the first set of one or more voltage pulses.
 2. The methodof claim 1, further comprising: re-applying the first set of one or morevoltage pulses to the piezoelectric device during a third time periodafter the second time period; and wherein the performance parameter ofthe piezoelectric device has a second value during the third timeperiod, and wherein a second difference between the second value and thereference value is less than a first difference between the first valueand the reference value.
 3. The method of claim 1, wherein theperformance parameter is a permittivity of the piezoelectric device. 4.The method of claim 1, wherein selectively applying the second set ofone or more voltage pulses comprises: applying a first voltage bias tothe piezoelectric device, wherein the first voltage bias has a firstpolarity; applying a second voltage bias to the piezoelectric deviceafter the first voltage bias has been applied, wherein the secondvoltage bias has a second polarity opposite the first polarity.
 5. Themethod of claim 4, wherein selectively applying the second set of one ormore voltage pulses further comprises: applying a third voltage bias tothe piezoelectric device after the first voltage bias has been appliedand before the second voltage bias is applied, wherein the third voltagebias is between the first voltage bias and the second voltage bias. 6.The method of claim 5, wherein the first voltage bias has a firstamplitude and the second voltage bias has a second amplitude, the secondamplitude is less than the first amplitude.
 7. The method of claim 6,wherein the second amplitude is less than or equal to an electriccoercive field voltage of the piezoelectric device, and wherein thefirst amplitude is greater than the electric coercive field voltage. 8.The method of claim 5, wherein the third voltage bias is zero.
 9. Asystem, comprising: a piezoelectric device disposed on a semiconductorsubstrate, the piezoelectric device comprising a piezoelectric structuredisposed between a first electrode and a second electrode; biascircuitry electrically coupled to the first electrode and the secondelectrode, wherein the bias circuitry is configured to apply a first setof one or more voltage pulses to the piezoelectric device over a firsttime period; measurement circuitry electrically coupled to the biascircuitry, wherein the measurement circuitry is configured to detectthat a performance parameter of the piezoelectric device has a firstvalue that exhibits a deviation from a reference value by more than apredetermined threshold value after application of the first set of oneor more voltage pulses.
 10. The system of claim 9, wherein the biascircuitry is configured to, based on detection of the deviation, performa recovery operation by selectively applying a second set of one or morevoltage pulses to the piezoelectric device over a second time period,the second time period being after the first time period and second setof one or more voltage pulses differing in magnitude and/or polarityfrom the first set of one or more voltage pulses.
 11. The system ofclaim 10, wherein the bias circuitry is further configured to re-applythe first set of one or more voltage pulses to the piezoelectric deviceduring a third time period after the second time period.
 12. The systemof claim 11, wherein the performance parameter of the piezoelectricdevice has a second value during the third time period, and wherein asecond absolute difference between the second value and the referencevalue is less than a first absolute difference between the first valueand the reference value.
 13. The system of claim 9, wherein themeasurement circuitry is configured to count a number of voltage biaspulses applied by the bias circuitry, and wherein the predeterminedthreshold value is a predetermined number of voltage bias pulses countedby the measurement circuitry.
 14. The system of claim 13, wherein themeasurement circuitry is configured to measure a total time that thebias circuitry is in a performance mode, and wherein the predeterminedthreshold value is a predetermined time measured by the measurementcircuitry.
 15. The system of claim 14, wherein the total time is atleast an hour.
 16. The system of claim 9, wherein a first magnitude ofthe first set of one or more voltage pulses is less than or equal to anelectric coercive field voltage of the piezoelectric structure.
 17. Asystem, comprising: a piezoelectric structure disposed between a firstelectrode and a second electrode; bias circuitry electrically coupled tothe first electrode and the second electrode, wherein the bias circuitryis configured to apply a first set of one or more voltage pulses to thepiezoelectric structure over a first time period; measurement circuitryelectrically coupled to the bias circuitry, wherein the measurementcircuitry is configured to determine whether the piezoelectric structurehas a first permittivity that exhibits a deviation from a referencepermittivity by more than a predetermined value; and wherein, upondetection of the deviation, the bias circuitry is configured to performa recovery operation by selectively applying a second set of one or morevoltage pulses to the piezoelectric structure over a second time period,the second time period being after the first time period and second setof one or more voltage pulses differing in magnitude and/or polarityfrom the first set of one or more voltage pulses.
 18. The system ofclaim 17, wherein the bias circuitry is further configured to re-applythe first set of one or more voltage pulses to the piezoelectricstructure during a third time period after the second time period. 19.The system of claim 18, wherein the piezoelectric structure has a secondpermittivity during the third time period, and wherein a second absolutedifference between the second permittivity and the referencepermittivity is less than a first absolute difference between the firstpermittivity and the reference permittivity.
 20. The system of claim 17,wherein the piezoelectric structure is arranged on a semiconductorsubstrate.